The invention relates to a method for using channels in a time-division multiple access (TDMA) radio system which comprises at least one base station and at least one mobile station and which operates on one or more carrier frequencies per base station, the carrier frequencies being divided into a plural number of physical channels comprising time slots, a predetermined number of time slots forming a frame, and in which system one of the base station""s carriers is a main carrier on which a main control channel (MCCH) operates.
In a time-division multiple access (TDMA) data transmission, one carrier frequency is used to provide a plural number of physical channels by dividing the data transmission taking place on the carrier into time slots and by always allocating regularly recurring time slots to a particular physical channel. Physical channels can be further used to form logical channels by reserving data transmission capacity from the physical channels to a logical channel.
For example, in a system conforming to the TETRA (Terrestrial Trunked Radio) standard where channels are formed by applying the TDMA method, one time slot comprises 510 bits. Four time slots form a frame, 18 frames form a multiframe and 60 multiframes form a hyperframe. In the TETRA system the logical channels to be used can be divided into two main categories: control channels (CCH), used for transmitting various control data, for example, and traffic channels (TCH), used for transmitting speech data, for example.
In the TETRA system a base station can use one or more carriers divided into physical channels as described above. One of the carriers is a main carrier comprising a Main Control Channel (MCCH) and possibly Secondary Control Channels (SCCH), if any are used. The MCCH is usually transmitted in the first time slot of a main carrier frame. At a small base station of a single carrier it is possible that also the first time slot of a frame is occasionally allocated to traffic channels. The MCCH is then only transmitted in frame 18 (control frame) of the multiframe, frame 18 being reserved exclusively for the transmission of control data. SCCH channels, if any, are sent in time slots 2, 3 and 4 (max. three) of the main carrier frame. To be able to operate on the main control channel of the base station, the mobile station must first receive a Sync-PDU (Protocol Data Unit) from a Broadcast Synchronisation Channel (BSCH). The Sync-PDU comprises the data of the colour code used by a base station cell, the code allowing the mobile station to decode the contents of other time slots. With the exception of the BSCH, the contents of the channels are coded by mean""s of a colour code. The Sync-PDU also comprises detailed information about the timing of the time slot, frame and multiframe used by the base station cell. After having received the Sync-PDU, the mobile station receives a Sysinfo-PDU from a Broadcast Network Channel (BNCH). The Sysinfo-PDU comprises, for example, information about whether the mobile station can operate in the cell concerned, and necessary values of parameters relating to the use of the cell. The BSCH and the BNCH are Broadcast Control Channels (BCCH), the channels broadcasting from one base station to all mobile stations within the area of the base station. After having received both the Sync-PDU and the Sysinfo-PDU, the mobile station is synchronized to the base station cell andi can potentially start to operate on its main control channel MCCH.
A problem with the above described arrangement is that if all the physical channels available on the main carrier have been allocated to traffic channels, the base station can transmit the BSCH and BNCH channels only once during one multiframe, in frame 18 (control frame) of the multiframe. The transmission time of a multiframe being about one second, this delays the synchronization of mobile stations to a base station cell since the mobile station is able to receive a BSCH only about once a second and a BNCH after a second from the BSCH. The synchronization can therefore take even two seconds, which is a long time, particularly if the mobile station must check several main carrier alternatives when evaluating their suitability for its operation.
An object of the invention is therefore to provide a method allowing the above problems to be solved. The objects of the invention are achieved with a method characterized in that at least one physical channel of a main carrier is used for transmitting broadcast control channels (BCCH), and the last one of said at least one physical channel is allocated to a traffic channel (TCH) only if other physical channels are not available at the base station.
The invention is based on the idea that one physical channel is kept available on the main carrier until all other physical channels are reserved, the physical channel on the main carrier being available to the base station for transmitting the BSCH and the BNCH.
An advantage of the method of the invention is that it accelerates the synchronization of the mobile station to the base station by allowing, at its best, the BSCH and the BNCH to be transmitted once during every frame, i.e. at intervals of about 60 ms.
The invention further relates to a method for using channels in a time-division multiple access (TDMA) radio system which comprises at least one base station and at least one mobile station and which operates on one or more carrier frequencies per base station, the carrier frequencies being divided into a plural number of physical channels comprising time slots, a predetermined number of time slots forming a frame, and in which system one of the base station""s carriers is a main carrier on which a main control channel (MCCH) operates, the method being characterized in that at least one physical channel of the main carrier is used for transmitting broadcast control channels (BCCH) and the last one of said at least one physical channel is allocated to a traffic channel (TCH) only if other carriers of the base station, which have at least one reserved physical channel, do not have any physical channels available.
The method allows the synchronization of a mobile station to a base station to be accelerated if unallocated physical channels are available, provided, however, that the number of carriers in active use is not increased, i.e. the aim is to have a minimum number of carriers in use.
The invention further relates to a method for using channels in a time-division multiple access (TDMA) radio system which comprises at least one base station and at least one mobile station and which operates on one or more carrier frequencies per base station, the carrier frequencies being divided into a plural number of physical channels comprising time slots, a predetermined number of time slots forming a frame, and in which system one of the base station""s carriers is a main carrier on which a main control channel (MCCH) operates, the method being characterized in that at least one physical channel of the main carrier not allocated for other use is used for transmitting broadcast control channels (BCCH), and channels are allocated base-station-specifically either by applying a first principle of allocation which primarily supports the minimizing of the synchronization delay of a mobile station to a base station, or a second principle of allocation which primarily supports the minimizing of the number of carriers in use at a base station.
The invention is based on that the system has two different channel allocation principles which it can apply. According to both allocation principles, a physical channel available on the main carrier is used for transmitting broadcast control channels, if possible. The different allocation principles allow a base-station-specific decision to be made on what is to be primarily emphasized: the minimizing of the synchronization delay or the minimizing of the number of carriers in use.
An advantage of the invention is that by selecting the desired channel allocation principle the system can be easily optimized to suit different circumstances and, in addition, the system accelerates the synchronization of a mobile station to a base station whenever the main carrier has a physical channel available that can be used for transmitting broadcast control channels.
The invention further relates to a a time-division multiple access (TDMA) radio system which comprises at least one base station and at least one mobile station and which operates on one or more carrier frequencies per base station, the carrier frequencies being divided into a plural number of physical channels comprising time slots, a predetermined number of time slots forming a frame, and in which system one of the base station""s carriers is a main carrier on which a main control channel (MCCH) operates, the system being characterized in that the system is arranged to use at least one physical channel of the main carrier for transmitting broadcast control channels (BCCH) and to allocate the last one of said at least one physical channel to a traffic channel (TCH) only if other physical channels are not available at the base station.
The invention further relates to a time-division multiple access (TDMA) radio system which comprises at least one base station and at least one mobile station and which operates on one or more carrier frequencies per base station, the carrier frequencies being divided into a plural number of physical channels comprising time slots, a predetermined number of time slots forming a frame, and in which system one of the base station""s carriers is a main carrier on which a main control channel (MCCH) operates, the system being characterized in that the system is arranged to use at least one physical channel of the main carrier for transmitting broadcast control channels (BCCH) and to allocate the last one of said at least, one physical channel to a traffic channel (TCH) only if the other carriers of the base station that have at least one reserved physical channel, do not have any physical channels available.
The invention further relates to a time-division multiple access (TDMA) radio system which comprises at least one base station and at least one mobile station and which operates on one or more carrier frequencies per base station, the carrier frequencies being divided into a plural number of physical channels comprising time slots, a predetermined number of time slots forming a frame, and in which system one of the base station""s carriers is a main carrier on which a main control channel (MCCH) operates, the system being characterized in that the system is arranged to use at each base station at least one physical channel of the main carrier not allocated for other use for transmitting broadcast control channels (BCCH), each base station having two alternative channel allocation principles to choose from; the first alternative allocation principle primarily supporting the minimizing of the synchronization delay of the mobile station to the base station and the second alternative allocation principle primarily supporting the minimizing of the number of carriers in use at the base station.
The above described radio systems allow the advantages of the methods of the invention to be easily gained.